Telephone system with auxiliary signaling circuit



Aug. 21, 1928. 1,681,246

- R. G. MCCURDY TELEPHONE SYSTEM WITH AUXILIARY SIGNALING CIRCUIT Filed Feb. 26, 1924 INVENTOR 1m Mam ATTORNEY Patented Aug. 21, 1928. v

j UNITED STATES} PATENT, QFFl-CE.

RALPH G. Mectrnmr, or nnepnwoon, NEW JERSEY, AssI Non'ro, AMERICAN rnonn AND TELEGRAPH, COMPANY, A conrozaarron on NEW YORK.

TELEPHONE sYsrn vr wm'n AUXILIARY SIGNALING olrtourr.

Application filed February 26, 1924. Serial No, 695 333.

An object of my invention. is toprovide a new and improved system of slgnalln circuits in a telephone system. Another o ject of my invention isto rovide a selective si u b naling system in such a way that there shall other objects o fmy invention will become apparent on consideration of the example of theinvention disclosed: in, the accompanying drawing, which is a diagram illustrating a,

central station andka subscribers station and a system of circuits appertaining thereto.

In many telephone systems, the talking is done over metallic circuits but an auxiliary circuit or auxiliary circuits are provided for signaling by using one or both conductor pairs of the metallic circuit for one side of the signaling circuit and using ground for the return. The ground connection sometimes causes noise in subscribers sets connected to exposed lines, due to the unbalance caused by the signaling apparatus and voltages to ground due to induction, or to potential differences between the central office ground and the ground at the subscribers premises. Where single-phase alternating current railway systems are employed in the neighborhood,false operation of subscribers bells may occur, due to induction or ground potential differences from the railway currents in the ground.

To obviate such difiiculties, I propose to utilize the cable sheath as the return conductor instead of the ground. Referring to the drawing, a central station is shown at Q, and a subscribers station at S. Extending for a considerable part of the way between them is a cable with the sheath A and within it a plurality of conductor pairs such as B, and

among these conductor pairs is one pair which leads to the subscribers station S.

The portion of the cable to which the letter A is applied isrepresented as underground. At D the cable is brought up above the ground and continued overhead as at F. The connection of the conductors is made in the box E and the sections of the sheath A and F are metallically connected by a jumper G.

In the neighborhood of the subscribers premises, a plurality of conductor pairs such as H are brought out from within the cable sheath F to the terminal board I, and one pair of conductors J goes from this board to the subscriberss set S.

Aseries of binding posts K is placed on the board'I and these are all connected bya conductor L to the cable sheath E. From one ofthese binding posts K, a. conductor M goes to the subscribers set S. i V A lightning arrester N'and fuses Oare pro vided for the pair of mailrconductors J and for the auxiliary conductor M. Y This lightning arrester has the usual connection to ground *as shown. i i

The subscribers bell P. is shown in the normal condition bridged across one of the conductors J and the conductor M. On lifting the receiver from the hook, the transmitter and receiver will be connected in the usual way across the two conductors J. h

At the central station the switch R is arranged for party ringing to apply ringing,

current to either conductor of the pair B leading to the substation S. One side of the ringing generator at the central station Q is grounded as shown, and the cable sheath is also connected to ground at the central station Q.

It will be seen that the cable sheath affords a metallic connection extending a large part of the way between the central station Q and the subscribers set S. This metallic connec tion is completed and extended by the jumper G, and the branch conductors L and M.

The beneficial efiect of this new arrangement on induced disturbances may be seen by reference to the drawing which shows a disturbing conductor X having a voltage V to ground, to which the aerial cable F is exposed. A capacity C exists between the disturbing conductor X and the sheath E and capacities C and C between the sheath and the two sides of the cable pair connecting the substation Sand the central oifice Q.

If the bell P be connected to ground in the usual manner there is a direct path to ground via the capacities C and C, in series, one wire and noise in the receiver will be due only to slight inequalities in the two sides of the pair and will be practically the same in magnitude as if the circuit were a single party line with the bell connected across the pair.

Potential diilt'erences in the ground between the central oilice and at the subscribers premises will have negligible effect on the signaling apparatus either with respect to noise or false signaling, because such potential difiercnces are not impressed on the signaling apparatus.

I claim:

1. In combination, two telephone stations, a conductor pair extending between them to form a talking circuit. signaling apparatus at both stations, other conductor pairs. all said conductor pairs being comprised in a cable with a metallic cable sheath, and said sheath forming With one of the conductors of said first mentioned pair a signaling circuit comprising said signaling apparatus.

2. In the transmission of speeh and signals in a telephone cable system. the method of obviating interference in transmitting the talking currents over a circuit; formed by z, conductor pair Within the cable. which consists in transmitting the signaling currents over a circuit formed by the cable sheath and one of the conductors of said pair.

3. In combination. two telephone stations. :1 cable sheath extendingbetween them. a conductor pair Within said sheath, a jumper metallieally connecting sections of the cable sheath, :1 subscribers set with branch conductors from said conductor pair within the sheath and from the sheath itself, and signaling ap 'mratus arranged tor connection during signaling periods in a. circuit ccnnprising the sheath and one of the comluetors of the pair within the sheath.

4. In combination, a central telephone station, a subscribers telephone station. a cable sheath extending between them, a conductor pair within it for voice currents. means to apply rineiirg current between the sheath and one conductor of the pair at the central station. and means normally connecting a bell between the same conductor of the pair and the sheath at the sul.)scribe1"s station.

In testimony whereof. I have signed my name to this specification this 25th day of February, 1924.

RALPH G. MCCURDY. 

